This invention relates to equipment for monitoring the electrical activity of the heart in a living body, and particularly to portable electrocardiograph monitors.
A number of portable devices exist for monitoring the electrical activity of the heart. U.S. Pat. No. 4,351,164 to Allain, Jr. discloses a self-powered life monitor in a pocket-sized, tubular container with electrode probes on one end which are capable of piercing the skin to rest in subcutaneous tissue and an LED light source on the other end to indicate the existence and strength of an electrical potential indicative of bioelectric activity.
Sarnoff et al., in U.S. Pat. No. 3,792,700, describes a handheld battery-operated cardiac monitor which converts a signal picked up by two spaced electrodes on the body to pulsing light or to an audible beeping signal indicative of the heart beat. The monitor is provided with a flashing lamp and audible monitor and is attached via two electrical leads to two electrodes placed in the user's armpits.
ECG telephone transmitters using armpit electrodes of the type shown in Sarnoff et al. are also known. The ECG signal is tone-frequency modulated for transmission along telephone lines.
U.S. Pat. No. 3,732,868 to Willems, et al. shows a device for the audible reproduction of an electrocardiogram signal with speech-like sounds. Three electrodes arranged in a triangular pattern are attached to the device housing by means of three L-shaped contact arms.
A number of cardiac monitoring devices are capable of being worn on the wrist of a user. One example of such a device is shown in U.S. Pat. No. 4,230,127 to Larson. This apparatus displays a count in beats per minute. The circuitry includes means for automatically turning the system off when no heartbeats are detected for a six-second interval.
During emergency medical diagnosis, an immediate record of the electrocardiogram (ECG) is highly desired to indicate if the victim has a major cardiac arrthymia such as tachycardia, fibrillation or asystole. Palpation of the pulse only indicates if the heart is or is not ejecting blood. The stethoscope can identify that the heart is or is not beating, but it cannot identify the nature of abnormal cardiac excitation and recovery. Only the ECG can provide this information. At present, no personal, pocket-sized ECG monitor for such a purpose exists.
Portable ECG monitors are also available with cathode-ray tube (CRT) display of the ECG. U.S. Pat. No. 3,848,582 to Milani et al. describes a CRT unit consisting of a battery-powered cathode ray oscilloscope in a metallic housing with pickup electrodes provided directly on the back of the housing and a pistol grip underneath the housing. It is not necessary to use electrode gel with this apparatus to insure proper contact with the patient's skin. The CRT display surface is on the order of 2 inches by 3 inches, and the total depth of the apparatus is approximately 6 to 8 inches. Although a CRT unit is relatively small and lightweight in comparison with the expensive and cumbersome devices used for ECG monitoring in hospitals, it is quite bulky and heavy compared to other portable cardiac monitors. Also, the high power consumption of the CRT causes excessively rapid battery drain which could lead to complete loss of power in a critical situation. This fact severely undermines the confidence which an emergency medical technician might have in using such an apparatus.
Shanks, in U.S. Pat. Nos. 4,250,503 and 4,346,378, describes a dot-matrix, liquid-crystal display (LCD) for display of sine waves and other continuous waveforms. A waveform to be displayed is periodically sampled using an A/D converter, and binary numbers representative of the amplitude of each sample are stored, either in a serial shift register or in a random-access memory (RAM). The stored information is then displayed at an appropriate rate for the LCD.
Liquid crystals with response time of less than 50 milliseconds are currently used in a miniature television manufactured by Seiko, according to an article entitled "Flat-screen color TV," by Herbert Shuldiner, published in the November, 1983 issue of Popular Science.